YOU may not think he knows your name or cabin number, but rest assured that if you give him a tip, he will know your name and cabin number. The stewards on HAL are remarkable about remember names/faces etc and if he personally cannot identify you one of his buddies can/will. The stewards then refer to a listing of who has removed the automatic tips from their account. IF they have some question and are not sure who you are (which is highly unlikely they cannot find out), they would opt to share into the pool rather than 'try to get away' with keeping it.

They like their jobs; they want to get re-hired for another contract; they want to get along with their fellow crewmembers; they are honest.